Abstract
Abstract. VHF Faraday rotation (FR) and amplitude scintillation data recorded simultaneously during May 1978–December 1980 at Delhi (28.63° N, 77.22° E; Dip 42.44° N) is analyzed in order to study the Faraday polarization fluctuations (FPFs) and their dependence on the occurrence of post sunset secondary maximum (PSSM) and amplitude scintillations. It is noted that FPFs are observed only when both PSSM and scintillations also occur simultaneously. FPFs are observed only during winter and the equinoctial months of high sunspot years. FPFs events are associated with intense scintillation activity, which is characterized by sudden onsets and abrupt endings, and are observed one to three hours after the local sunset. When FPFs and scintillation data from Delhi is compared with the corresponding data from a still lower latitude station, Hyderabad (17.35° N, 78.45° E), it is found that the occurrence of FPFs and scintillations at Delhi is conditional to their prior occurrence at Hyderabad, which indicates their production by a plasma bubble and the as-sociated irregularities generated initially over the magnetic equator. In addition, FPFs and scintillation data for October 1979, when their occurrence was maximum, is also examined in relation to daytime (11:00 LT) electrojet strength (EEj) values and evening hour h’F from an equatorial location, Kodaikanal (10.3° N, 77.5° E). It is interesting to note that FPFs and scintillations are most likely observed when the EEj was 100 nT or more and h’F reaches around 500 km. These results show that EEj and evening hours h’F values over the magnetic equator are important parameters for predicting FPFs and scintillation activity at locations such as Delhi, where scintillation activity is much more intense as compared to the equatorial region due to the enhanced back-ground ionization due to the occurrence of PSSM.Key words. Ionosphere (equatorial ionosphere; ionospheric irregularities) – Radio science (ionospheric physics)
Highlights
Faraday rotation and amplitude scintillation data for the period May 1978–December 1980, obtained from VHF telemetry transmissions from geostationary satellites, such as Symphonie-II (May 1978–April 1979) at 137 MHz andGupta et al.: Faraday polarization fluctuationsETS-II (May 1979–December 1980) at 136 MHz recorded at National Physical Laboratory (NPL), Delhi, have been utilized for the present study
To examine the relationship between the occurrence of post sunset secondary maximum (PSSM), Faraday polarization fluctuations (FPFs) and scintillations with daytime electrojet strength variation, the electrojet strength is calculated using the scheme suggested by Chandra and Rastogi (1974) and the detailed procedure is described by Gupta and Singh (2000) and the references therein
The results obtained from Faraday rotation (FR) and the amplitude monitored at Delhi during high solar activity shows that: 1. The occurrence of FPFs at Delhi is conditional to the simultaneous occurrence of both PSSM and scintillations
Summary
Faraday rotation and amplitude scintillation data for the period May 1978–December 1980, obtained from VHF telemetry transmissions from geostationary satellites, such as Symphonie-II (May 1978–April 1979) at 137 MHz and. ETS-II (May 1979–December 1980) at 136 MHz recorded at National Physical Laboratory (NPL), Delhi, have been utilized for the present study. No data could be recorded during the months of March 1980, and September 1979 and 1980 due to satellite ecliptic conditions. The days for which both FR and amplitude data are available at NPL have been considered for the present study. Ionosonde h’F data from an equatorial station of Kodaikanal (dip 3.5◦) has been utilized
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